As ink-jet printers that eject ink droplets to a recording medium, such as a recording sheet, an ink-jet printer including a conveying mechanism that conveys a recording sheet, and an ink-jet head having an ink ejection surface in which a number of nozzles that eject ink droplets to the recording sheet conveyed by the conveying mechanism are disposed is known. A number of individual ink channels that lead from an outlet of a common ink chamber through pressure chambers to the nozzles are formed inside the ink-jet head. Further, the ink-jet head has an actuator that individually applies ejection energy to the ink within each pressure chamber according to an instruction from a control device. As such an ink-jet head, there is an ink-jet head in which a number of nozzles are disposed in a matrix in a conveying direction of a recording sheet, and in a direction orthogonal to the conveying direction in the ink ejection surface in order to enhance the density of ejection channels of ink droplets. Such ink-jet printer is disclosed in, for example, JP-A-2006-044113.
According to the above ink-jet printer, only from a viewpoint of the enhancement of the density of ejection channels of ink droplets, a number of nozzles are disposed in a matrix in the ink ejection surface. Therefore, the positions of the nozzles in the conveying direction of a recording sheet are determined regardless of the control period of the control device for ink ejection. For this reason, for example, when the resolution of a printing image in the conveying direction of a recording sheet is changed, the control period and the timing with which an ink droplets are ejected to positions on the recording sheet where dots are to be formed may not coincide with each other. In this case, the positions of dots to be formed on the recording sheet in the conveying direction of the recording sheet vary, and thereby printing quality deteriorates. In order to solve this problem, it is considered that the control period of the control device is further shortened. However, it is necessary to further improve the processing speed of the control device in shortening the control period, and consequently, the cost of the control device becomes high.